Tubular strings are formed with threaded connections made up at the surface with tongs and then run in downhole to a desired location. More recently the assembled tubular string is expanded after it is properly positioned downhole. The string can be expanded into another preexisting string already in the wellbore that can have a bell at the lower end so that after expansion both connected strings have a common inside diameter. Other configurations can occur that call for expansion of all or part of a tubular string where the length of the expansion includes the threaded joints that connect the tubulars that make up the string.
The problem that occurs when a threaded connection is expanded and some separation occurs in the thread to make it no longer gas tight. One reason for this is the tendency of the box and pin ends to curl as a reaction to the expansion force at the noses of the pin and the box. Solutions to address this problem have been proposed particularly at the pin end that focused on pre-stressing the pin end by bending it on makeup from the longitudinal axis with a groove formed at the base of the box. The box end was cantilevered on a fulcrum with the idea that expansion would make the box nose curl in against the pin while the retention of the pin nose by a groove in the box base would prevent curling in of the pin nose. These approaches to sealing the ends of a thread both against pressure within the tubular and pressure on the outside facing the annular space in a wellbore are illustrated in U.S. Pat. No. 7,585,002. The retention device for the pin end that was located on the box was a reverse shoulder 26. Its purpose was to plastically deform the pin end so that at a location away from the pin end a part of the pin wall could contact the box wall for sealing.
Another approach in the context of a two step thread was to put resilient seals between the steps and to further provide in association with the seals between the steps mating wicker surfaces with the idea that the expansion would squeeze the resilient seal and the wicker surfaces would hold together better than smooth overlapping surfaces that got pushed together as a swage was advanced through the threaded connection. Variations on this approach are illustrated in U.S. Pat. No. 6,792,665. One of the issues with resilient seals is temperature service limit. In deeper wells the operating temperatures can exceed 150° C. which approached or exceeded the service limit of most seal materials such as elastomers. The other issue was a lack of residual contact pressure in the area between the thread steps after expansion that limited the effectiveness of a metal to metal seal in that area. The radial expansion resulted in wall thinning to conserve volume and as result the force holding the mating metal surfaces between thread steps was reduced. A more effective way to hold the thread together during and after expansion was needed that would take into account the axial dimension changes that resulted from radial expansion as well as changes in wall dimensions. In the past, leakage has resulted from expansion of threaded connections because of the resulting pin and box separation along the thread as a result of the expansion process.
Still other designs relating to expanding threaded connections are illustrated in: U.S. Pat. No. 5,462,315; US 2007/0035131A1; U.S. Pat. No. 6,554,287B1; US 2003/0067166A1; US 2005/0236834A1;
U.S. Pat. Nos. 5,415,442 and 6,322,110. At least some of these references show the opposed projections on the pin and the box that overlap each other and contact upon makeup or on expansion. The present invention addresses this need by providing a mechanism to retain the connection together despite expansion where, in one embodiment, the threaded connection is retained together between steps while the retention device allows for relative axial movement between the pin and the box.
The present invention is for a connection that does not necessarily have to be expanded. The features of the invention can be employed to enhance sealing in a threaded connection even for connections that are simply threaded together with tongs and run into a subterranean location. These and other features of the present invention will become more apparent to those skilled in the art by a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.
The following US Patents and Applications illustrate known thread forms that can be used in conjunction with the present invention: 2008/0277933; U.S. Pat. Nos. 7,588,269 and 6,254,146.